Isolation and characterization of the dimetal decacarbonyl dication [Ru(CO)] and the metal-only Lewis-pair [Ag{Ru(CO)}] .

The reaction of Ag with Ru(CO) in a CO atmosphere under concommittant irradiation with UV-light yields a salt of the metal-only Lewis-pair [Ag{Ru(CO)}]. Switching the silver cation for a more process-selective deelectronator yields a salt of the homoleptic transition metal carbonyl cation [Ru(CO)], which fills the gap between the known cations [Ru(CO)] and [Ru(CO)]. The amount of π-backdonation in this series was studied by a combination of vibrational spectroscopy and computed relaxed force constants.

Accessing unusual heterocycles: ring expansion of benzoborirenes by formal cycloaddition reactions.

Benzoborirenes are a very rare class of strained boron heterobicyclic systems. In this study a kinetically stabilized benzoborirene 1 is shown to react with multiple bonds of trimethylphosphine oxide, acetaldehyde, and -butyl isonitrile. The (2 + 2) cycloaddition product with trimethylphosphine oxide, benzo[][1,2,5]oxaphosphaborole, has a long apical PO bond (194.

Synthesis, Reactivity and Coordination Chemistry of Group 9 PBP Boryl Pincer Complexes: [(PBP)M(PMe)] (M = Co, Rh, Ir; = 1, 2).

The unsymmetrical diborane(4) derivative [(d(CHP(Pr))abB)-Bpin] () proved to be a versatile PBP boryl pincer ligand precursor for Co(I) (, ), Rh(I) (-) and Ir(I/III) (-, -) complexes, in particular of the types [(d(CHP(Pr))abB)M(PMe)] (-) and [(d(CHP(Pr))abB)M-PMe] (-). Whilst similar complexes have been obtained before, for the first time, the coordination chemistry of a homologous series of PBP pincer complexes, in particular the interconversion of the five- and four-coordinate complexes -/-, was studied in detail. For Co, instead of the mono phosphine complex , the dinitrogen complex [(d(CHP(Pr))abB)Co(N)(PMe)] () is formed spontaneously upon PMe abstraction from in the presence of N.

Cyclopropylmethyldiphosphates are substrates for sesquiterpene synthases: experimental and theoretical results.

New homo-sesquiterpenes are accessible after conversion of presilphiperfolan-8β-ol synthase (BcBOT2) with cyclopropylmethyl analogs of farnesyl diphosphate, and this biotransformation is dependent on subtle structural refinements. Two of the three cyclisation products are homo variants of germacrene D and germacrene D-4-ol while the third product reported contains a new bicyclic backbone for which no analogue in nature has been described so far. The findings on diphosphate activation are discussed and rationalised by relaxed force constants and dissociation energies computed at the DFT level of theory.

Cis- and trans-binding influences in [NUO·(N)].

Uranium nitride-oxide cations [NUO] and their complexes with equatorial N ligands, [NUO·(N)] (n = 1-7), were synthesized in the gas phase. Mass-selected infrared photodissociation spectroscopy and quantum chemical calculations confirm [NUO·(N)] to be a sterically fully coordinated cation, with electronic singlet ground state of A, linear [NUO] core, and C structure. The presence of short N-U bond distances and high stretching modes, with slightly elongated U-O bond distances and lowered stretching modes, is rationalized by attributing them to cooperative covalent and dative [ǀN≡U≡Oǀ] triple bonds.

How Strong is a Reverse Dative Bond? Compliance Constants as Unique Bond Strength Descriptors.

The concepts of bond strength and bond order are at the very heart of chemistry. Nevertheless, the study of local mechanical bond strengths in large polyatomic molecules is a nontrivial task. In a recent publication, Peters and Lehnert et al.

Masked Amino Trimethyl Lock (H N-TML) Systems: New Molecular Entities for the Development of Turn-On Fluorophores and Their Application in Hydrogen Sulfide (H S) Imaging in Human Cells.

Masked trimethyl lock (TML) systems as molecular moieties enabling the bioresponsive release of compounds or dyes in a controlled temporal and spatial manner have been widely applied for the development of drug conjugates, prodrugs or molecular imaging tools. Herein, we report the development of a novel amino trimethyl lock (H N-TML) system as an auto-immolative molecular entity for the release of fluorophores. We designed Cou-TML-N and MURh-TML-N , two azide-masked turn-on fluorophores.

Antibiotic Conjugates with an Artificial MECAM-Based Siderophore Are Potent Agents against Gram-Positive and Gram-Negative Bacterial Pathogens.

The development of novel drugs against Gram-negative bacteria represents an urgent medical need. To overcome their outer cell membrane, we synthesized conjugates of antibiotics and artificial siderophores based on the MECAM core, which are imported by bacterial iron uptake systems. Structures, spin states, and iron binding properties were predicted using density functional theory.

Biomimetic enterobactin analogue mediates iron-uptake and cargo transport into and .

The design, synthesis and biological evaluation of the artificial enterobactin analogue and several fluorophore-conjugates thereof are described. provides an attachment point for cargos such as fluorophores or antimicrobial payloads. Corresponding conjugates are recognized by outer membrane siderophore receptors of Gram-negative pathogens and retain the natural hydrolyzability of the tris-lactone backbone.

Experimental and theoretical characterization of the strong effects on DNA stability caused by half-sandwich Ru(II) and Ir(III) bearing thiabendazole complexes.

The synthesis and characterization of two half-sandwich complexes of Ru(II) and Ir(III) with thiabendazole as ancillary ligand and their DNA binding ability were investigated using experimental and computational methods. H NMR and acid-base studies have shown that aquo-complexes are the reactive species. Kinetic studies show that both complexes bind covalently to DNA through the metal site and non covalently through the ancillary ligand.

Novel atrazine-binding biomimetics inspired to the D1 protein from the photosystem II of Chlamydomonas reinhardtii.

Biomimetic design represents an emerging field for improving knowledge of natural molecules, as well as to project novel artificial tools with specific functions for biosensing. Effective strategies have been exploited to design artificial bioreceptors, taking inspiration from complex supramolecular assemblies. Among them, size-minimization strategy sounds promising to provide bioreceptors with tuned sensitivity, stability, and selectivity, through the ad hoc manipulation of chemical species at the molecular scale.

Kinetic Studies of Donor-Acceptor Cyclopropanes: The Influence of Structural and Electronic Properties on the Reactivity.

The kinetics of (3+2) cycloaddition reactions of 18 different donor-acceptor cyclopropanes with the same aldehyde were studied by in situ NMR spectroscopy. Increasing the electron density of the donor residue accelerates the reaction by a factor of up to 50 compared to the standard system (donor group=phenyl), whereas electron-withdrawing substituents slow down the reaction by a factor up to 660. This behavior is in agreement with the Hammett substituent parameter σ.

Structural Elucidation of Trace Components Combining GC/MS, GC/IR, DFT-Calculation and Synthesis-Salinilactones, Unprecedented Bicyclic Lactones from Salinispora Bacteria.

The analysis of volatiles released by marine Salinispora bacteria uncovered a new class of natural compounds displaying an unusual bicyclic [3.1.0]-lactone skeleton.

The Interstitial Carbon of the Nitrogenase FeMo Cofactor is Far Better Stabilized than Previously Assumed.

The first quantum-mechanical calculations of all relevant potential constants in both the iron-molybdenum cofactor and the iron-vanadium cofactor of nitrogenase suggest that the carbide is bound to the center of the enzyme much more strongly than hitherto assumed. Previous studies seemed to indicate a dummy function of the interstitial carbon, with a weak force constant (ca. 0.

The Weakness of B-H⋅⋅⋅π Interactions: Much Softer than a Hydrogen Bond.

Recently, a new type of non-covalent interaction, the B-H⋅⋅⋅π interaction, was introduced. Nevertheless, the unique determination of individual, non-covalent bond strengths in complex molecular systems is a non-trivial task with often controversial results. The utilization of generalized compliance constants (relaxed force constants) is proposed as unique bond-strength descriptors for classical and non-classical hydrogen bonds.

Correction: Effective in silico prediction of new oxazolidinone antibiotics: force field simulations of the antibiotic-ribosome complex supervised by experiment and electronic structure methods.

[This corrects the article DOI: 10.3762/bjoc.12.

Effective in silico prediction of new oxazolidinone antibiotics: force field simulations of the antibiotic-ribosome complex supervised by experiment and electronic structure methods.

We propose several new and promising antibacterial agents for the treatment of serious Gram-positive infections. Our predictions rely on force field simulations, supervised by first principle calculations and available experimental data. Different force fields were tested in order to reproduce linezolid's conformational space in terms of a) the isolated and b) the ribosomal bound state.

Molecular recognition of naphthalene diimide ligands by telomeric quadruplex-DNA: the importance of the protonation state and mediated hydrogen bonds.

In depth Monte Carlo conformational scans in combination with molecular dynamics (MD) simulations and electronic structure calculations were applied in order to study the molecular recognition process between tetrasubstituted naphthalene diimide (ND) guests and G-quadruplex (G4) DNA receptors. ND guests are a promising class of telomere stabilizers due to which they are used in novel anticancer therapeutics. Though several ND guests have been studied experimentally in the past, the protonation state under physiological conditions is still unclear.

Comment on "The Nature of the Fourth Bond in the Ground State of C2: The Quadruple Bond Conundrum".

Is it time to reconsider the whole concept of quadruple bonding? Contrary to the conclusion of Shaik and co-workers in Chem. Eur. J.

Oligoene-Based π-Helicenes or Dispiranes? Winding up Oligoyne Chains by a Multiple Carbopalladation/Stille/(Electrocyclization) Cascade.

A domino approach consisting of up to five consecutive steps to access either highly substituted dispiranes or π-helicenes from oligoyne chains is reported. The domino sequence consists of several carbopalladation reactions, a Stille cross-coupling to obtain the helicenes, and, depending on the steric demands of the helicene, a final 6π-electrocyclization to afford the dispiranes. Formally, the latter transformation contravenes the Woodward-Hoffmann rules, as revealed by X-ray crystallography of the dispirane.

III-defined concepts in chemistry: rigid force constants compliance constants as bond strength descriptors for the triple bond in diboryne.

In a recent publication, the interpretation of Braunschweig's diboryne NHC-BB-NHC as a true triple bond is questioned. The analysis by Köppe and Schnöckel is based, , on the calculation of rigid coupling force constants. Nevertheless, since it is known for a long time that the use of rigid force constants as bond strength descriptors is by no means straightforward, we recomputed the rigid force constants for a model diboryne, applying different coordinate systems and compared the values with the relaxed force constants (generalized compliance constants, GCC).

Sigillin A, a unique polychlorinated arthropod deterrent from the snow flea Ceratophysella sigillata.

The snow flea Ceratophysella sigillata, a winter-active species of springtail, produces unique polychlorinated octahydroisocoumarins to repel predators. The structure of the major compound, sigillin A, was elucidated through isolation, spectroscopic analysis, and X-ray crystallography. Sigillin A showed high repellent activity in a bioassay with predatory ants.

π-Helicenes truncated to a minimum: access through a domino approach involving multiple carbopalladations and a Stille coupling.

A novel type of π-helicenes is reported, in which the π-system is truncated to an all-s-cis all-Z oligoene chain. A domino sequence was developed, consisting of up to four consecutive carbopalladation reactions and a terminal Stille cross-coupling, to generate these entities in one step from the respective linear oligoynes. Despite the minimal π-system, very high optical rotation values were encountered for the single enantiomers.

Preparation, structural properties and thermal isomerization of hex-3-ene-1,5-diyne bridged [2.2]paracyclophanes.

The [2.2]paracyclophane moiety is used as a spacer to connect the ends of a hex-3-ene-1,5-diyne unit, a π-system that on thermolysis usually cycloaromatizes to a benzene ring (Bergman cyclization). For the preparation of the pseudo-geminally-bridged system 9, the diacetylene 3 was chain-extended to the diol 16, which after conversion to the pseudo-geminal dibromide 17 was ring-closed by treatment with LiHMDS/HMPA to the [2.